WO2021106727A1

WO2021106727A1 - Negative electrode for nonaqueous electrolyte secondary batteries, nonaqueous electrolyte secondary battery, and method for producing negative electrode for nonaqueous electrolyte secondary batteries

Info

Publication number: WO2021106727A1
Application number: PCT/JP2020/043101
Authority: WO
Inventors: 文一水越; 敬光田下
Original assignee: 三洋電機株式会社
Priority date: 2019-11-29
Filing date: 2020-11-19
Publication date: 2021-06-03
Also published as: CN114730854A; US20220416245A1; JPWO2021106727A1

Abstract

The purpose of the present disclosure is to provide a negative electrode for nonaqueous electrolyte secondary batteries, said negative electrode being capable of suppressing a decrease in the high-rate charge/discharge cycle characteristics. A negative electrode for nonaqueous electrolyte secondary batteries according to one embodiment of the present disclosure is provided with: a negative electrode collector; a first negative electrode mixture layer that is arranged on the surface of the negative electrode collector; and a second negative electrode mixture layer that is arranged on the surface of the first negative electrode mixture layer. The first negative electrode mixture layer contains a first negative electrode active material and a first water-soluble polymer material; and the second negative electrode mixture layer contains a second negative electrode active material and a second water-soluble polymer material. The ratio of the amount (S1) of the first water-soluble polymer material present on the surface of the first negative electrode active material to the amount (V1) of the first water-soluble polymer material present in voids among particles of the first negative electrode active material, namely S1/V1 is larger than the ratio of the amount (S2) of the second water-soluble polymer material present on the surface of the second negative electrode active material to the amount (V2) of the second water-soluble polymer material present in voids among particles of the second negative electrode active material, namely S2/V2.

Description

Method for manufacturing negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and negative electrode for non-aqueous electrolyte secondary battery

The present disclosure relates to a method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a negative electrode for a non-aqueous electrolyte secondary battery.

The negative electrode constituting the non-aqueous electrolyte secondary battery generally has a negative electrode current collector and a negative electrode mixture layer formed on both sides of the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material and a binder, and the structure of the negative electrode mixture layer is formed by binding the particles of the negative electrode active material to each other and the negative electrode active material and the negative electrode current collector. It is maintained.

Patent Documents 1 and 2 disclose a method of adhering a binder to the surface of a negative electrode active material by dry-mixing the negative electrode active material with a binder and then producing a slurry. As a result, Patent Document 1 describes that the binding force between the negative electrode active materials and between the negative electrode active material layer and the negative electrode current collector can be increased, so that the cycle characteristics are improved. It is stated that the charging / discharging efficiency is improved by the binder holding the electrolytic solution.

JP-A-2002-42787 Japanese Unexamined Patent Publication No. 2005-166446

By the way, when a non-aqueous electrolyte secondary battery is used as a power source for an electric vehicle (EV) or the like, charging / discharging is often performed at a high rate. Be done. However, in the negative electrode mixture layer containing the negative electrode active material in which a large amount of the binder is adhered to the surface, the permeability of the electrolytic solution is not good, so that the high rate charge / discharge cycle characteristics may be deteriorated.

Therefore, an object of the present disclosure is to provide a negative electrode for a non-aqueous electrolyte secondary battery capable of suppressing a decrease in high-rate charge / discharge cycle characteristics.

The negative electrode for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, is provided on the surfaces of the negative electrode current collector, the first negative electrode mixture layer provided on the surface of the negative electrode current collector, and the first negative electrode mixture layer. A second negative electrode mixture layer provided is provided. The first negative electrode mixture layer contains a first negative electrode active material and a first water-soluble polymer material, and the second negative electrode mixture layer contains a second negative electrode active material and a second water-soluble polymer material. The ratio of the amount (S1) of the first water-soluble polymer material present on the surface of the first negative electrode active material to the amount (V1) of the first water-soluble polymer material present in the interparticle voids of the first negative electrode active material ( S1 / V1) is the amount of the second water-soluble polymer material present on the surface of the second negative electrode active material with respect to the amount of the second water-soluble polymer material (V2) present in the interparticle voids of the second negative electrode active material. It is characterized in that it is larger than the ratio (S2 / V2) of (S2).

The non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by comprising the negative electrode for the non-aqueous electrolyte secondary battery, the positive electrode, and the non-aqueous electrolyte.

In the method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, a first negative electrode mixture slurry prepared by kneading a first negative electrode active material and a first water-soluble polymer material is collected as a negative electrode. The first negative electrode mixture layer forming step of applying to the surface of the body to form the first negative electrode mixture layer, and the second negative electrode combination prepared by kneading the second negative electrode active material and the second water-soluble polymer material. Shearing when the first negative electrode mixture slurry is kneaded, including a second negative electrode mixture layer forming step of applying the agent slurry to the surface of the first negative electrode mixture layer to form a second negative electrode mixture layer. The force is larger than the shearing force when the second negative electrode mixture slurry is kneaded.

According to one aspect of the present disclosure, it is possible to provide a non-aqueous electrolyte secondary battery capable of suppressing a decrease in high-rate charge / discharge cycle characteristics.

FIG. 1 is a vertical sectional view of a cylindrical secondary battery which is an example of the embodiment. FIG. 2 is a cross-sectional view of a negative electrode which is an example of the embodiment. FIG. 3A is a schematic view showing an example of a cross section of the first negative electrode mixture layer, and FIG. 3B is a schematic view showing an example of a second negative electrode mixture layer.

As described above, there is known a method of adhering a binder to the surface of a negative electrode active material by dry-mixing the negative electrode active material with a binder and then producing a slurry. Since a water-soluble polymer material such as a binder can retain an electrolytic solution, the water-soluble polymer material adheres to the surface of the negative electrode active material, so that a carbon material or the like having poor affinity with the electrolytic solution, etc. The electrolytic solution can be brought into contact with the surface of the negative electrode active material of. However, according to the studies by the present inventors, it has been found that the high rate charge / discharge cycle characteristics may be deteriorated in the negative electrode mixture layer containing the negative electrode active material in which the water-soluble polymer material is adhered to the surface. It is considered that this is because the permeability of the electrolytic solution on the surface of the negative electrode is lowered, so that the distribution of the electrolytic solution in the negative electrode becomes non-uniform during charging and discharging. Therefore, as a result of diligent studies by the present inventors, a water-soluble polymer material is used as the negative electrode active material so that the negative electrode mixture layer is made into two layers and the layer on the outer surface side in contact with the electrolytic solution has good permeability of the electrolytic solution. A large amount of water-soluble polymer material is present on the surface of the negative electrode active material so that the inner layer in contact with the negative electrode current collector has a large amount of water-soluble polymer material in the interparticle voids of the negative electrode. I came up with the idea of a negative electrode for batteries. According to this negative electrode, it is possible to provide a non-aqueous electrolyte secondary battery capable of suppressing a decrease in high-rate charge / discharge cycle characteristics.

Hereinafter, an example of an embodiment of the cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, the specific shape, material, numerical value, direction, etc. are examples for facilitating the understanding of the present invention, and can be appropriately changed according to the specifications of the cylindrical secondary battery. .. Further, the exterior body is not limited to the cylindrical type, and may be, for example, a square type. Further, in the following description, when a plurality of embodiments and modifications are included, it is assumed from the beginning that the characteristic portions thereof are appropriately combined and used.

FIG. 1 is an axial sectional view of a cylindrical secondary battery 10 which is an example of an embodiment. In the secondary battery 10 shown in FIG. 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an exterior body 15. The electrode body 14 has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound via the separator 13. In the following, for convenience of explanation, the sealing body 16 side will be referred to as “top” and the bottom side of the exterior body 15 will be referred to as “bottom”.

The inside of the secondary battery 10 is sealed by closing the opening end of the exterior body 15 with the sealing body 16.

Insulating plates

17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through the through hole of the insulating plate 17 and is welded to the lower surface of the filter 22 which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends to the bottom side of the exterior body 15 through the through hole of the insulating plate 18 and is welded to the inner surface of the bottom portion of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as a negative electrode terminal. When the negative electrode lead 20 is installed at the terminal portion, the negative electrode lead 20 passes through the outside of the insulating plate 18 and extends to the bottom side of the exterior body 15 and is welded to the inner surface of the bottom portion of the exterior body 15.

The exterior body 15 is, for example, a bottomed cylindrical metal exterior can. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the internal airtightness of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16 and is formed by pressing, for example, a side surface portion from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and the sealing body 16 is supported on the upper surface thereof via the gasket 27.

The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are laminated in order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their central portions, and an insulating member 24 is interposed between the peripheral portions thereof. When the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 breaks, which causes the upper valve body 25 to swell toward the cap 26 side and separate from the lower valve body 23, thereby cutting off the electrical connection between the two. .. When the internal pressure further rises, the upper valve body 25 breaks and gas is discharged from the opening 26a of the cap 26.

Hereinafter, the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte constituting the secondary battery 10 will be described in detail, and in particular, the negative electrode active material contained in the negative electrode mixture layer 32 constituting the negative electrode 12 will be described in detail.

[Negative electrode]
FIG. 2 is a cross-sectional view of the negative electrode 12 which is an example of the embodiment. The negative electrode 12 includes a negative electrode current collector 30, a first negative electrode mixture layer 32a provided on the surface of the negative electrode current collector 30, and a second negative electrode mixture layer provided on the surface of the first negative electrode mixture layer 32a. 32b and the like. The thicknesses of the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b may be the same or different from each other.

As the negative electrode current collector 30, for example, a metal foil that is stable in the potential range of the negative electrode such as copper, a film in which the metal is arranged on the surface layer, or the like is used. The thickness of the negative electrode current collector 30 is, for example, 5 μm to 30 μm. The first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b (hereinafter, the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b may be collectively referred to as the negative electrode mixture layer 32) are negative electrode active. Includes substances and water-soluble polymeric materials. Further, the negative electrode mixture layer 32 may contain a binder. Examples of the binder include fluorine-based resin, PAN, polyimide-based resin, acrylic-based resin, polyolefin-based resin, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), and the like. These may be used alone or in combination of two or more.

The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions reversibly, and includes, for example, graphite particles, a Si-based material, a metal alloying with lithium such as tin (Sn), or a metal element such as Sn. Examples include alloys and oxides. The negative electrode active material preferably contains graphite particles. The content of graphite particles in the negative electrode active material can be, for example, 90% by mass to 100% by mass.

The graphite particles are not particularly limited, such as natural graphite and artificial graphite, but artificial graphite is preferable. _{The surface spacing (d 002} ) of the (002) plane of the graphite particles used in the present embodiment by the X-ray wide-angle diffraction method is preferably, for example, 0.3354 nm or more, and more preferably 0.3357 nm or more. Further, it is preferably less than 0.340 nm, and more preferably 0.338 nm or less. The crystallite size (Lc (002)) of the graphite particles used in the present embodiment determined by the X-ray diffraction method is, for example, preferably 5 nm or more, more preferably 10 nm or more, and more preferably 10 nm or more. It is preferably 300 nm or less, and more preferably 200 nm or less. When the interplanar spacing (d ₀₀₂ ) and the crystallite size (Lc (002)) satisfy the above ranges, the battery capacity of the secondary battery 10 tends to be larger than when the above ranges are not satisfied.

Graphite particles can be produced, for example, as follows. Coke (precursor), which is a main raw material, is crushed to a predetermined size, aggregated with a flocculant, and then fired at a temperature of 2600 ° C. or higher in a block-shaped pressure-molded state to be graphitized. The graphitized block-shaped molded product is pulverized and sieved to obtain graphite particles having a desired size. Here, the internal porosity of the graphite particles can be adjusted by adjusting the particle size of the pulverized precursor, the particle size of the agglomerated precursor, and the like. For example, the average particle size of the precursor after pulverization (median diameter D50 in terms of volume, the same applies hereinafter) is preferably in the range of 12 μm to 20 μm. Further, the internal porosity of the graphite particles can be adjusted by the amount of the volatile component added to the block-shaped molded product. When a part of the coagulant added to the coke (precursor) volatilizes during firing, the coagulant can be used as a volatile component. Pitch is exemplified as such a flocculant.

Further, the graphite particles may be produced, for example, as follows. Coke (precursor), which is the main raw material, is crushed to a predetermined size, and in a state where they are agglomerated with a coagulant such as pitch, they are calcined at a temperature of 2600 ° C. or higher, graphitized, and then sieved. Graphite particles of the desired size can be obtained. Here, the internal porosity of the graphite particles can be adjusted by adjusting the particle size of the pulverized precursor, the particle size of the agglomerated precursor, and the like. For example, the average particle size of the precursor after pulverization is preferably in the range of 12 μm to 20 μm.

The water-soluble polymer material is preferably a material that acts as a thickener for the slurry. The water-soluble polymeric material may act as a binder. The water-soluble polymer material may be, for example, carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt). ), Polyvinyl alcohol (PVA) and the like. These may be used alone or in combination of two or more.

Next, the negative electrode active material and the water-soluble polymer material in the negative electrode mixture layer 32 will be described with reference to FIG. FIG. 3A is a schematic view showing an example of a cross section of the first negative electrode mixture layer, and FIG. 3B is a schematic view showing an example of a second negative electrode mixture layer. As shown in FIG. 3A, the first negative electrode mixture layer 32a contains the first negative electrode active material 34a and the first water-soluble polymer material 36a. Further, as shown in FIG. 3B, the second negative electrode mixture layer 32b contains the second negative electrode active material 34b and the second water-soluble polymer material 36b. The amount of the first water-soluble polymer material 36a (S1) present on the surface of the first negative electrode active material 34a with respect to the amount (V1) of the first water-soluble polymer material 36a existing in the interparticle voids of the first negative electrode active material 34a. ) (S1 / V1) is the second negative electrode active material 34b present on the surface of the second negative electrode active material 34b with respect to the amount (V2) of the second water-soluble polymer material 36b present in the interparticle voids of the second negative electrode active material 34b. It is larger than the ratio (S2 / V2) of the amount (S2) of the water-soluble polymer material 36b. That is, in the first negative electrode mixture layer 32a, most of the first water-soluble polymer material 36a is present on the surface of the first negative electrode active material 34a, and in the second negative electrode mixture layer 32b, the second water-soluble polymer material 36b. Most of them are present in the interparticle voids of the second negative electrode active material 34b. With this configuration, it is possible to improve the permeability of the electrolytic solution of the negative electrode mixture layer 32 while increasing the binding force between the negative electrode current collector 30 and the negative electrode mixture layer 32, so that the high rate charge / discharge cycle characteristics of the battery can be deteriorated. It can be suppressed. At the same time, it is possible to suppress a decrease in low-rate charge cycle characteristics. Here, the amount of the water-soluble polymer material present in the interparticle voids of the negative electrode active material or on the surface of the negative electrode active material is a two-dimensional value obtained by measuring the cross section of the negative electrode mixture layer 32. For each of the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b, the water-soluble polymer material existing on the surface of the negative electrode active material and the water-soluble material existing in the interparticle voids of the negative electrode active material are performed by the following procedure. By visualizing the polymer material, it is possible to compare S1 / V1 and S2 / V2.

<Measuring method of S1 / V1 and S2 / V2>
(1) The cross section of the negative electrode mixture layer is exposed. Examples of the method for exposing the cross section include a method in which a part of the negative electrode is cut out and processed with an ion milling device (for example, IM4000PLUS manufactured by Hitachi High-Tech) to expose the cross section of the negative electrode mixture layer.
(2) Using SEM-EDX (for example, Flat QUAD manufactured by Bruker), the elements derived from the water-soluble polymer material are mapped in the cross section of the exposed negative electrode mixture layer, and the first negative electrode mixture is prepared. Images of each of the layer 32a and the second negative electrode mixture layer 32b are taken. Here, the element derived from the water-soluble polymer material is a characteristic element contained in the water-soluble polymer material. For example, if the water-soluble polymer material is a Na salt of CMC, the Na element is mapped. Can be done. The measurement conditions for the cross section of the negative electrode mixture layer are as follows, for example.
Cross-section magnification: 800 times Electron acceleration voltage: 5 kV
Emission current: 10 μA
Probe current: High
Condenser lens: 1.0
Capture time: 180 sec
(3) If possible, S1 / V1 and S2 / V2 may be visually compared from the images obtained from each of the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b. Each image may be binarized using image analysis software (for example, ImageJ manufactured by the National Institutes of Health) to quantify S1 / V1 and S2 / V2 for comparison.

The first negative electrode active material 34a and the second negative electrode active material 34b may be the same. Further, the first water-soluble polymer material 36a and the second water-soluble polymer material 36b may be the same. By sharing the materials contained in the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b, the cost can be reduced. Further, even if the materials contained in the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b are shared, the method for producing the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b can be used as described later. By making the difference, the relationship of S1 / V1> S2 / V2 can be satisfied.

At least one of the first negative electrode active material 34a and the second negative electrode active material 34b may contain a Si-based material. The Si-based material is a material capable of reversibly occluding and releasing lithium ions, and functions as a negative electrode active material. Examples of the Si-based material include Si, an alloy containing Si, and _{a silicon oxide such as SiO X} (X is 0.8 to 1.6). The Si-based material is a negative electrode material capable of improving the battery capacity as compared with the negative electrode active material. From the viewpoint of improving the battery capacity and suppressing the deterioration of the high rate charge / discharge cycle characteristics, the content of the Si-based material in the first negative electrode active material 34a or the second negative electrode active material 34b is, for example, 0.5% by mass to 10% by mass. It is preferably by mass%, more preferably 3% by mass to 7% by mass.

Next, a method for manufacturing the negative electrode 12 will be described. In the method of manufacturing the negative electrode 12, the first negative electrode mixture slurry prepared by kneading the first negative electrode active material 34a and the first water-soluble polymer material 36a is applied to the surface of the negative electrode current collector 30 to apply the first negative electrode. The first negative electrode mixture is prepared by kneading the first negative electrode mixture layer forming step for forming the mixture layer 32a and the second negative electrode active material 34b and the second water-soluble polymer material 36b. It includes a second negative electrode mixture layer forming step of applying to the surface of the agent layer 32a to form the second negative electrode mixture layer 32b.

The first negative electrode mixture slurry can be prepared, for example, as follows.
(1) The first negative electrode active material 34a and the first water-soluble polymer material 36a are mixed to prepare a first mixture.
(2) An appropriate amount of solvent is added to the first mixture and kneaded. The solvent is, for example, water. The amount of the solvent to be added is, for example, 10% by mass to 30% by mass with respect to the total amount of the first negative electrode active material 34a and the first water-soluble polymer material 36a.
(3) A binder such as styrene-butadiene copolymer rubber (SBR) is added to the first mixture. Further, the first mixture is stirred to prepare the first negative electrode mixture slurry.

The second negative electrode mixture slurry can be prepared, for example, as follows.
(1) The second water-soluble polymer material 36b and the solvent are mixed to prepare a second mixture. The solvent is, for example, water. The amount of the solvent is, for example, 40% by mass to 60% by mass with respect to the total amount of the second water-soluble polymer material 36b and the second negative electrode active material 34b to be added next.
(2) The second negative electrode active material 34b is added to the second mixture.
(3) The second mixture is kneaded. A solvent may be additionally added as appropriate during kneading.
(4) Add the binder to the second mixture. Further, the second mixture is stirred to prepare the second negative electrode mixture slurry.

The shear force when kneading the first negative electrode mixture slurry is larger than the shear force when kneading the second negative electrode mixture slurry. As a result, in the second negative electrode mixture layer 32b, a large amount of the second water-soluble polymer material 36b is arranged in the interparticle voids of the second negative electrode active material 34b, and in the first negative electrode mixture layer 32a, the first water-soluble polymer material A large amount of 36a is arranged on the surface of the first negative electrode active material 34a. According to this configuration, the permeability of the electrolytic solution of the second negative electrode mixture layer on the outer surface side in contact with the electrolytic solution and the adhesion between the first negative electrode mixture layer and the negative electrode current collector 30 are improved, so that the secondary is secondary. The deterioration of the high rate charge / discharge cycle characteristics of the battery 10 is suppressed. When at least one of the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b contains a Si-based material having a large expansion and contraction due to charging and discharging, the above effect is remarkably exhibited. In the present disclosure, "kneading" means mixing a mixture containing a negative electrode active material, a water-soluble polymer, and a solvent so as to apply a shearing force.

Then, the first negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 30 and dried (first negative electrode mixture layer forming step), and then the second negative electrode mixture slurry is placed on the first negative electrode mixture layer 32a. Is applied to both sides and dried (second negative electrode mixture layer forming step). Further, the negative electrode mixture layer 32 can be formed by rolling the first negative electrode mixture layer 32a and the second negative electrode mixture layer 32b with a rolling roller. The second negative electrode mixture slurry can also be applied onto the first negative electrode mixture layer 32a before drying.

[Positive electrode]
The positive electrode 11 is composed of a positive electrode current collector such as a metal foil and a positive electrode mixture layer formed on the positive electrode current collector. As the positive electrode current collector, a metal foil such as aluminum that is stable in the potential range of the positive electrode, a film in which the metal is arranged on the surface layer, or the like can be used. The positive electrode mixture layer contains, for example, a positive electrode active material, a binder, a conductive agent, and the like.

For the positive electrode 11, for example, a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. is applied onto a positive electrode current collector and dried to form a positive electrode mixture layer, and then the positive electrode mixture layer is applied. It can be produced by rolling.

Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides, for example, _{_{_{_{Li x CoO 2, Li x NiO}}}} 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1- _{_{_{_{y M y O z, Li x}}}} Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M; Na, Mg, Sc, Y, Mn, Fe, Co, Ni , Cu, Zn, Al, Cr, Pb, Sb, B, 0 <x ≦ 1.2, 0 <y ≦ 0.9, 2.0 ≦ z ≦ 2.3). These may be used alone or in admixture of a plurality of types. In that it can increase the capacity of the nonaqueous electrolyte secondary battery, the positive electrode active _{_{_{_{material, Li x NiO 2, Li x}}}} Co y Ni 1-y O 2, Li x Ni 1-y M y O z ( M; At least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 <x≤1.2, 0 <y≤0. It is preferable to contain a lithium nickel composite oxide such as 9.9, 2.0 ≦ z ≦ 2.3).

Examples of the conductive agent include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, and graphite. These may be used alone or in combination of two or more.

Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used alone or in combination of two or more.

[Separator]
For the separator 13, for example, a porous sheet having ion permeability and insulating property is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose and the like are suitable. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Further, a multilayer separator containing a polyethylene layer and a polypropylene layer may be used, or a separator 13 coated with a material such as an aramid resin or ceramic may be used.

[Non-aqueous electrolyte]
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to the liquid electrolyte (electrolyte solution), and may be a solid electrolyte using a gel polymer or the like. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen substituent in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine.

Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and methylpropyl carbonate. , Ethylpropyl carbonate, chain carbonate such as methyl isopropyl carbonate, cyclic carboxylic acid ester such as γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, etc. Chain carboxylic acid ester and the like can be mentioned.

Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahexyl, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4. -Cyclic ethers such as dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether , Dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxy toluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxy Chain ethers such as ethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc. Kind and so on.

As the halogen substituent, it is preferable to use a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, a fluorinated chain carboxylic acid ester such as methyl fluoropropionate (FMP), or the like. ..

The electrolyte salt is preferably a lithium salt. _Examples of the lithium _{_{_{salt, LiBF 4, LiClO 4, LiPF}}} 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, Li (P (C 2 O 4) F 4), LiPF _6-x (C _n F _{2n + 1} ) _x (1 <x <6, n is 1 or 2), LiB ₁₀ Cl ₁₀ , LiCl, LiBr, LiI, lithium _{chloroborane, lithium lower aliphatic carboxylate, Li 2} B ₄ O ₇ , borates such as Li (B (C ₂ O ₄ ) F ₂ ), LiN (SO ₂ CF ₃ ) ₂ , LiN (C ₁ F _{2l + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) {l , M is an integer of 1 or more} and other imide salts. As the lithium salt, these may be used individually by 1 type, or a plurality of types may be mixed and used. _{Of these, LiPF 6} is preferably used from the viewpoint of ionic conductivity, electrochemical stability, and the like. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the solvent.

Hereinafter, the present disclosure will be further described with reference to Examples, but the present disclosure is not limited to these Examples.

<Example>
[Preparation of positive electrode]
Aluminum-containing lithium nickel cobalt oxide (LiNi _0.88 Co _0.09 Al _0.03 O ₂ ) was used as the positive electrode active material. The positive electrode active material is mixed so as to be 100 parts by mass, graphite as a conductive agent is 1 part by mass, and polyvinylidene fluoride powder as a binder is 0.9 parts by mass, and further, N-methyl-2-pyrrolidone (NMP) is mixed. ) Was added in an appropriate amount to prepare a positive electrode mixture slurry. This slurry is applied to both sides of a positive electrode current collector made of aluminum foil (thickness 15 μm) by the doctor blade method, the coating film is dried, and then the coating film is rolled by a rolling roller to cover both sides of the positive electrode current collector. A positive electrode having a positive electrode mixture layer formed therein was produced.

[Preparation of negative electrode]
First, a first negative electrode mixture slurry was prepared. Graphite particles were mixed so as to be 95 parts by mass and SiO was 5 parts by mass, and this was used as a negative electrode active material. 100 parts by mass of the negative electrode active material and 1 part by mass of carboxymethyl cellulose (CMC) were mixed, and 20 parts by mass of water was added to the mixture and kneaded. After further adding 1 part by mass of styrene-butadiene copolymer rubber (SBR) to this mixture, the mixture was stirred to prepare a first negative electrode mixture slurry.

Next, a second negative electrode mixture slurry was prepared. First, 50 parts by mass of water and 1 part by mass of CMC were mixed, and 100 parts by mass of the negative electrode active material was added to the mixture and kneaded. A second negative electrode mixture slurry was prepared by further adding 1 part by mass of SBR to this mixture and then stirring the mixture. The shearing force when kneading the first negative electrode mixture slurry was larger than the shearing force when kneading the second negative electrode mixture slurry.

The first negative electrode mixture slurry was applied to both sides of the negative electrode current collector made of copper foil by the doctor blade method and dried to form the first negative electrode mixture layer. Further, the above-mentioned second negative electrode mixture slurry was applied onto the first negative electrode mixture layer and dried to form a second negative electrode mixture layer. At this time, the coating mass ratio of the first negative electrode mixture slurry and the second negative electrode mixture slurry per unit area was set to 5: 5. The first negative electrode mixture layer and the second negative electrode mixture layer were rolled by a rolling roller to prepare a negative electrode. When the cross section of the negative electrode was observed, it was S1 / V1> S2 / V2.

[Preparation of non-aqueous electrolyte]
5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a non-aqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed so as to have a volume ratio of 1: 3, and LiPF ₆ Was dissolved at a concentration of 1.5 mol / L, and this was used as a non-aqueous electrolyte.

[Manufacturing of non-aqueous electrolyte secondary battery]
(1) A positive electrode lead is attached to a positive electrode current collector, a negative electrode lead is attached to a negative electrode current collector, and then a separator made of a polyethylene microporous film is wound between the positive electrode and the negative electrode to form a winding type. The electrode body of was prepared.
(2) Insulating plates were arranged above and below the electrode body, the negative electrode lead was welded to the exterior body, the positive electrode lead was welded to the sealing body, and the electrode body was housed in the exterior body.
(3) After injecting the non-aqueous electrolyte into the exterior body by a decompression method, the open end of the exterior body was sealed with a sealing body via a gasket, and this was used as a non-aqueous electrolyte secondary battery.

<Comparative example 1>
The same procedure as in the Examples was carried out except that the second negative electrode mixture layer was formed using the first negative electrode mixture slurry.

<Comparative example 2>
The same procedure as in the Examples was carried out except that the first negative electrode mixture layer was formed using the second negative electrode mixture slurry.

<Comparative example 3>
The same procedure as in the Examples was carried out except that the first negative electrode mixture layer was formed using the second negative electrode mixture slurry and the second negative electrode mixture layer was formed using the first negative electrode mixture slurry.

[Measurement of capacity retention rate in high rate cycle]
Under an environmental temperature of 25 ° C., the non-aqueous electrolyte secondary batteries of each example and each comparative example were charged at 1 C (4600 mA) with a constant current up to 4.2 V, and then at 4.2 V with a constant voltage up to 1/50 C. Charged. Then, at 0.5C, a constant current was discharged to 2.5V. This charging / discharging was regarded as one cycle, and 100 cycles were performed. The capacity retention rate of the non-aqueous electrolyte secondary battery of each Example and each Comparative Example in the high rate cycle was determined by the following formula.
Capacity retention rate = (Discharge capacity in the 100th cycle / Discharge capacity in the 1st cycle) x 100

[Measurement of capacity retention rate in initial low rate cycle]
Under an environmental temperature of 25 ° C., the non-aqueous electrolyte secondary batteries of each example and each comparative example were charged at 0.3 C (1380 mA) at a constant current to 4.2 V, and then charged at 4.2 V to 1/50 C. It was charged at a constant voltage. Then, at 0.5C, a constant current was discharged to 2.5V. This charge / discharge was regarded as one cycle, and 50 cycles were performed. The capacity retention rate in the high-rate charge / discharge cycle of the non-aqueous electrolyte secondary battery of each Example and each Comparative Example was determined by the following formula.
Capacity retention rate = (Discharge capacity in the 50th cycle / Discharge capacity in the 1st cycle) x 100

[Measurement of capacity retention rate in low-rate charge / discharge cycle]
Under an environmental temperature of 25 ° C., the non-aqueous electrolyte secondary batteries of each example and each comparative example were charged at 0.3 C (1380 mA) at a constant current to 4.2 V, and then charged at 4.2 V to 1/50 C. It was charged at a constant voltage. Then, at 0.5C, a constant current was discharged to 2.5V. This charge / discharge was regarded as one cycle, and 500 cycles were performed. The capacity retention rate in the high-rate charge / discharge cycle of the non-aqueous electrolyte secondary battery of each Example and each Comparative Example was determined by the following formula.
Capacity retention rate = (Discharge capacity in the 500th cycle / Discharge capacity in the 1st cycle) x 100

Table 1 summarizes the results of capacity retention rates in various charge / discharge cycles of the non-aqueous electrolyte secondary batteries of Examples and Comparative Examples. The higher the value of the capacity retention rate in the charge / discharge cycle, the more the deterioration of the charge / discharge cycle characteristics was suppressed.

The secondary battery of the example had a higher capacity retention rate than the secondary battery of the comparative example in any cycle test, and the high rate charge / discharge cycle characteristic was particularly good as compared with the comparative example. This is because, in the negative electrode mixture layer of the example, the outer surface side layer in contact with the electrolytic solution has improved permeability of the electrolytic solution, and the inner layer in contact with the negative electrode current collector has adhesion to the negative electrode current collector. Is considered to have been improved.

10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 exterior body, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved part, 22 filter, 23 lower valve Body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening, 27 gasket, 30 negative electrode current collector, 32 negative electrode mixture layer, 32a first negative electrode mixture layer, 32b second negative electrode mixture layer, 34a 1st negative electrode active material, 34b 2nd negative electrode active material, 36a 1st water-soluble polymer material, 36b 2nd water-soluble polymer material

Claims

A negative electrode current collector, a first negative electrode mixture layer provided on the surface of the negative electrode current collector, and a second negative electrode mixture layer provided on the surface of the first negative electrode mixture layer are provided.
The first negative electrode mixture layer contains a first negative electrode active material and a first water-soluble polymer material.
The second negative electrode mixture layer contains a second negative electrode active material and a second water-soluble polymer material.
The amount of the first water-soluble polymer material (S1) present on the surface of the first negative electrode active material with respect to the amount (V1) of the first water-soluble polymer material present in the interparticle voids of the first negative electrode active material. ) Is the ratio (S1 / V1) of the second negative electrode active material present on the surface of the second negative electrode active material with respect to the amount (V2) of the second water-soluble polymer material present in the interparticle voids of the second negative electrode active material. 2 A negative electrode for a non-aqueous electrolyte secondary battery, which is larger than the ratio (S2 / V2) of the amount of the water-soluble polymer material (S2).
At least one of the first negative electrode active material and the second negative electrode active material contains a Si-based material, and the content of the Si-based material is the first negative electrode active material containing the Si-based material or the first negative electrode active material. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, which is 0.5% by mass to 10% by mass with respect to the mass of the negative electrode active material.
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2.
With the positive electrode
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte.
A first negative electrode mixture formed by applying a first negative electrode mixture slurry prepared by kneading a first negative electrode active material and a first water-soluble polymer material to the surface of a negative electrode current collector to form a first negative electrode mixture layer. The agent layer formation step and
A second negative electrode mixture slurry prepared by kneading a second negative electrode active material and a second water-soluble polymer material is applied to the surface of the first negative electrode mixture layer to form a second negative electrode mixture layer. 2 Including the negative electrode mixture layer forming step and
A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, wherein the shearing force when kneading the first negative electrode mixture slurry is larger than the shearing force when kneading the second negative electrode mixture slurry.